Sputter ripples and radiation-enhanced surface kinetics on Cu(001)

We have measured the temperature and flux dependence of the wavelength of surface ripples spontaneously formed by low-energy sputtering of a Cu(001) surface. We find that the temperature dependence of the ripple wavelength is non-Arrhenius, with a greater apparent activation at high temperature than at low temperature. Furthermore, the dependence of the wavelength on flux changes significantly with temperature. In the high-temperature regime, the wavelength decreases as the ion flux increases, while at low temperature, the wavelength is essentially independent of flux. We explain these results by a quantitative model that includes the mechanisms controlling the concentration of mobile defects on the surface in the two temperature regimes. At low temperature, mobile defects are induced by the ion beam while at higher temperature, the defects are thermally generated.

Figure 1

AFM image of an ion sputtered surface with $T=425\mathrm{K}$, $f=2.13\times {10}^{14}\text{ions}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. The total sputtering time is 9000 s. The white arrow on the AFM image indicates the direction of the ion beam and the [100] crystalline direction. The size of the image is $10\times 10\mu \mathrm{m}$. The graph beside shows the evolution of PSD of the surface during sputtering, measured by LiSSp.

Figure 2

Temperature dependence of the ion-induced ripple wavelength with $f=2.13\times {10}^{14}\text{ions}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. Two sets of results for ripples produced with the projected ion beam parallel to [100] and [110] direction are shown.

Figure 3

Flux dependence of ripples wavelength at (a) $T=481\mathrm{K}$, and (b) $T=409\mathrm{K}$. The ripples lie along the [100] direction.

Figure 4

Schematic representation of defect generation and diffusion processes included in our model.

Figure 5

The boundary in temperature and flux phase space separates different kinetic regimes in defect formation. The curve is calculated based on Eq. (8) with kinetic parameter of a Cu(001) surface.